1. Field of the Invention
The present invention relates to a tube connection structure for connecting a tube member formed with a passage for introducing and discharging a fluid, to a fluid pressure-operated apparatus such as an ON/OFF valve and a cylinder.
2. Description of the Related Art
Conventionally, the fluid pressure-operated apparatus such as an ON/OFF valve and a cylinder is provided with a tube connection structure for connecting a tube member. Such a tube connection structure is exemplified by a connection structure for a resin tube, as disclosed in Japanese Patent No. 2562781.
As shown in FIG. 10 the connection structure 1 comprises a cylindrical projection 3 which is disposed at an end of a cylindrical main joint body 2 and which extends along an outer circumferential surface of the main joint body 2. An annular long groove 4 is formed between the cylindrical projection 3 and the outer circumferential surface of the main joint body 2. A diametrally expanded section 6 is formed at an end of a resin tube 5 which is a tube member. The diametrally expanded section 6 is forcibly inserted into the annular long groove 4, and an end of the cylindrical projection 3 and an outer circumferential portion of the resin tube 5 are welded by using a resin material 7. Thus, the main joint body 2 and the resin tube 5 are fixed. The main joint body 2 and the resin tube 5 are sealed by an inner circumferential surface of a rising section 8 of the diametrally expanded section 6 and a tapered surface 9 of the main joint body 2 corresponding thereto.
However, the connection structure 1 for the resin tube concerning the conventional technique described above adopts a method in which the resin tube 5 is directly installed to a main fluid pressure-operated apparatus body. It is impossible to confirm the amount of insertion of the diametrally expanded section 6 of the resin tube 5 with respect to the annular long groove 4. For this reason, any dispersion occurs in the amount of insertion of the diametrally expanded section 6. Therefore, if the diametrally expanded section 6 is not sufficiently inserted into the annular long groove 4, the sealing is incomplete between the tapered surface 9 of the main joint body 2 and the rising section 8 of the resin tube 5. It is feared that the fluid, which flows through the inside of the resin tube 5, leaks out to the outside through any gap formed between the tapered surface 9 and the rising section 8.
Further, it is difficult to confirm whether or not the diametrally expanded section 6 of the resin tube 5 is uniformly formed in the circumferential direction. If the diametrally expanded section 6 is not formed uniformly, then any gap is formed between the rising section 8 and the tapered surface 9, and the sealing is incomplete. Also in this situation, a problem arises in that the fluid leaks out.
A general object of the present invention is to provide a tube connection structure of a fluid pressure-operated apparatus, which makes it possible to improve the operability to connect a tube member, and which makes it possible to reliably avoid any occurrence of defective sealing.
The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.